Force input coverage to be only a byte in gpu shaders.

src/gpu/gl/builders/GrGLVertexShaderBuilder.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrGLVertexShader_DEFINED
 #define GrGLVertexShader_DEFINED
 
@@ skipping 24 matching lines @@
     /*
      * Internal call for GrGLProgramBuilder.addVarying
      */
     void addVarying(const char* name, GrGLVarying*);
 
     /*
      * private helpers for compilation by GrGLProgramBuilder
      */
     void setupLocalCoords();
     void transformGLToSkiaCoords();
+    void setupBuiltinVertexAttribute(const char* inName, GrGLSLExpr1* out);
     void setupBuiltinVertexAttribute(const char* inName, GrGLSLExpr4* out);
     void emitAttributes(const GrGeometryProcessor& gp);
     void transformSkiaToGLCoords();
     void bindVertexAttributes(GrGLuint programID);
     bool compileAndAttachShaders(GrGLuint programId, SkTDArray<GrGLuint>* shaderIds) const;
 
     // an internal call which checks for uniquness of a var before adding it to the list of inputs
     bool addAttribute(const GrShaderVar& var);
     struct AttributePair {
         void set(int index, const SkString& name) {
             fIndex = index; fName = name;
         }
         int      fIndex;
         SkString fName;
     };
 
     GrGLShaderVar*                      fPositionVar;
     GrGLShaderVar*                      fLocalCoordsVar;
     int                                 fEffectAttribOffset;
 
     friend class GrGLProgramBuilder;
 
     typedef GrGLShaderBuilder INHERITED;
 };
 
 #endif